The present invention relates to an ignition coil device for an internal combustion engine, and more particularly to a connecting portion between an ignition cable and a high tension terminal which is connected to a secondary output terminal of an ignition coil.
A configuration of a conventional ignition coil device for an internal combustion engine is shown in FIG. 5. Reference numeral 1 denotes an outer casing of an ignition coil which is formed of a synthetic resin material, and this outer casing 1 has a projection la. Numeral 2 denotes a tubular high tension terminal embedded in the projection la. This tubular high tension terminal 2 is connected to a secondary output terminal 3 for outputting a secondary voltage occurring in an unillustrated ignition coil, and is provided with an annular recess 2a. It should be noted that the connection between the secondary output terminal 3 and the high tension terminal 2 is effected by welding, soldering or the like. Numeral 4 denotes a tubular terminal caulked at a tip of an ignition cable 5 for supplying the secondary voltage to an unillustrated ignition plug. This tubular terminal 4 has an annular protrusion 4a. It should be noted that the recess 2a constitutes a retaining portion for preventing the ignition cable 5 from coming off the high tension terminal 2. Namely, the conventional ignition coil device for an internal combustion engine is arranged such that the ignition cable 5 is inserted into the tubular portion of the high tension terminal 2 to allow the projection 4a to be fitted in the recess 2a, and the connecting portion is subsequently covered with a protection cap 6 formed of rubber or the like.
Since the conventional ignition coil device for an internal combustion engine is arranged as described above, there has been a problem in that component parts vibrate by mechanical vibrations during the operation of the internal combustion engine, and a gap is caused between the high tension terminal 2 and the terminal 4 due to a difference in natural vibration, thereby making it impossible to maintain the contact between the terminals 2 and 4 in a satisfactory state.
To overcome this drawback, an ignition coil for an internal combustion engine disclosed in, for example, Japanese Patent Unexamined Publication (Kokai) Sho-63-116414/(1988) has been proposed. FIG. 6 shows a configuration of the ignition coil for an internal combustion engine proposed in the above-mentioned publication. In FIG. 6, component parts or portions that are denoted by the same reference numerals as those of FIG. 5 show component parts or portions identical or equivalent to those of FIG. 5. In FIG. 6, reference numeral 7 denotes an ignition plug; 8, a terminal of the ignition plug 7; and 9, an electrically conductive coil spring in which a portion of its inside diameter is made to conform to the outside diameter of the terminal 8. Namely, the ignition coil for an internal combustion engine shown in FIG. 6 is designed to absorb vibrations of component parts caused by the mechanical vibrations during the operation of the internal combustion engine by means of the conductive coil spring.
With the ignition coil shown in FIG. 6, however, the high tension terminal 2 and the conductive coil spring 9 are merely in contact with each other only at a left end of the conductive coil spring 9. Accordingly, there has been a drawback in that the high tension terminal 2 and the conductive coil spring 9 repeat contact and non-contact due to the difference in natural vibration between the ignition coil for an internal combustion engine and the conductive coil spring 9.
In addition, with the ignition coil shown in FIG. 6, other drawbacks are encountered in that the conductive coil spring 9 comes off during an assembling operation, and that a mating component of the conductive coil spring 9 is required to have a predetermined shape, i.e., the outside diameter of the terminal 8 is required to conform to an inside-diameter portion of the conductive coil spring 9.